To fold newspapers, magazines, brochures, and the like, the sheets to be folded or the layers of sheets to be folded, which lie one on top of another, are passed through between a pair of cylinders, consisting of a folding blade cylinder and a folding jaw cylinder, in a folding apparatus. Such a folding jaw cylinder has one or more folding jaws, which extend in the longitudinal direction of the cylinder and form a folding jaw gap, into which a folding blade arranged at the folding jaw cylinder penetrates, with a stop extending in parallel to them. The layers of printed product, mostly layers of paper, which are located at this point of the pair of cylinders, are now pressed into the gap at the folding jaw cylinder. The folding blade is subsequently withdrawn, and the folding jaw gap is closed to the extent that the printed product layers, now folded, are held firmly and are carried during the revolution of the folding jaw cylinder. Via a clamp mechanism, consisting mostly of a cam and a cam roller rolling on it, the gap width between the folding jaw and the stop is controlled such that the printed product layers can be pressed by the folding blade into the gap and clamped between the folding jaw and the stop after withdrawal of the folding blade. Besides this rhythmic changing of the gap width, a so-called working distance can be set between the folding jaws and the actually associated stops for adjustment to different numbers or thicknesses of printed product layers.
A device for adjusting this working distance during the operation of the machine has been known from DE 38 38 314 A1. The folding jaw cylinder has two hollow cylinders here, which are rotatably mounted around a common axis. A folding jaw, extending in the axial direction, is arranged on the circumference of one of the hollow cylinders, and a counterjaw, acting as a stop and facing the folding jaw, is arranged at the other hollow cylinder. The folding jaw is mounted rotatably for rhythmically adjusting the gap width and consequently for gripping the paper, while the counterjaw is attached rigidly. To adjust the working distance between the folding jaw and the counterjaw, the two hollow cylinders are pivotable against each other on a common cylinder shaft. To achieve this, the two hollow cylinders are rotated symmetrically in relation to one another via a gear mechanism, so that the respective folding jaws and counterjaws move toward or away from one another in the manner of tongs. It is to be ensured by the simultaneous and symmetrical adjustment of both hollow cylinders that the folding jaws and their respective counterjaws are arranged symmetrically to the advancing folding blades. The gear mechanism for adjusting the two hollow cylinders has an adjusting shaft, which is guided by the hollow cylinder shaft, and whose rotary movement is deflected by 90.degree. each via two bevel gear sets and transmitted to an adjusting spindle, which has left-handed threads at one end zone and right-handed threads at the other end zone. Each threaded section is connected to one of the two hollow cylinders, so that the two hollow cylinders can be pivoted symmetrically in relation to one another by rotating the adjusting spindle, and the distance between the folding jaws and counterjaws can be adjusted as a result. The working distance is adjusted in this prior-art device as a junction of a continuous current measurement of the thickness of the printed product to be folded. Such a thickness-measuring device and the associated control devices are complicated and expensive. Furthermore, such a continuous adjustment of the working distance includes continuous regulation even in the case of thickness deviations that are within the permissible tolerance range. However, the continuous readjustments lead to a continually changing contact pressure in the area of the effective contact pressure between the folding jaw and the stop, as a consequence of which loss of printed copies or damage to printed copies may arise.
Another device for adjusting the working distance between the folding jaws and counterjaws of a folding jaw cylinder has been known from DE 40 37 130 A1. The folding jaw cylinder is likewise composed for this purpose of two hollow cylinders, at which the respective folding jaws and counterjaws are arranged in the known manner. The symmetrical, tong-like rotary movement of the two hollow cylinders takes place via complex gear mechanisms in this case.
A folding jaw cylinder likewise with two hollow cylinders, which can be rotated symmetrically and in a tong-like manner in relation to one another, at which the folding jaws are arranged rotatably and the counterjaws, rigidly, was disclosed in DE 40 35 617 A1. The device used in this prior-art folding jaw cylinder to adjust the working distance between the folding jaws and the respective counterjaws contains a sliding block, which can be displaced radially in relation to the cylinder axis. The two grooves of the sliding block extend in the shape of a V in relation to one another. A pin is rigidly attached to one of the hollow cylinders and is guided in the two grooves. The two hollow cylinders are rotated symmetrically to one another and, as a result, the working distance between the folding jaws and counterjaws is changed by the displacement of the sliding block in the radial direction toward or away from the cylinder axis.
The disadvantage of this prior-art folding jaw cylinders is the complicated design with two hollow cylinders, which must be manufactured separately and subsequently assembled. The mechanism known from DE 38 38 314 A1 for the mutual adjustment of the two hollow cylinders with adjusting shafts extending through the hollow cylinders, with bevel gear sets for deflecting the rotary movements and with the adjusting spindle is complicated, expensive, and susceptible to malfunction. Reliable self-locking of the adjusting spindle cannot be guaranteed. The gear mechanism arranged within the hollow cylinders according to DE 32 20 414 A1 is also complicated and expensive because of the multiple gear deflections. Problems arise in the solution according to DE 40 35 617 because of the contact pressure acting on the sliding block in the grooves. Such an adjustment inherently leads to clearance in a relatively short time, so that accurate adjustment of the working distance between the folding jaws and counterjaws is no longer guaranteed. In addition, the cleaning of such adjusting mechanisms, arranged in the hollow cylinder, requires complete disassembly of the cylinder in the case of contamination as a consequence of the oil and paper dust escaping massively in the folding apparatus. Contaminations represent a particular problem because of the risk of jamming, which may easily occur in these adjusting mechanisms because of the complex design with long operating chains, i.e., with multiple deflections, transmissions, sliding blocks, etc.
A one-part folding jaw cylinder is disclosed in DE 32 20 4 14 A1. The folding jaw and the movable counterjaw can be adjusted here to the paper thickness to be processed. The counterjaw is displaceable via two eccentric bolts approximately in the circumferential direction of the folding jaw cylinder and as a result, it can be adjusted to a defined value in relation to the folding blade. The folding jaw, controlled via a cam roller, is fastened with screws to a spindle, which is mounted on both sides in the cylinder body of the folding jaw cylinder. To adjust the working distance between the folding jaw and the counterjaw, not only is the counterjaw displaced, but the folding jaw is also rotated in relation to the cylinder. The connection between the folding jaw and the cam roller must be interrupted for this purpose, and the part of the connection carrying the folding jaw must be made rotatable and lockable via another system of eccentric bolts in relation to the part carrying the cam roller. Adjustment of the working distance is possible only when the press has stopped, and it requires the adjustment of the eccentric bolts of the folding jaws and counterjaws one by one. An adjusting mechanism for coordinating the adjusting movements of the counterjaw and the folding jaw is not provided.